Linear air diffusers and vents are well known. The simplest of these have fixed outlets directing the flow of the supplied air. However, it is often desirable to be able to preferentially direct discharge of the supply air, depending upon whether the room is to be cooled or heated. For example, for the efficient cooling of a warm room, it is desirable to direct the discharge of the cool supply air horizontally along the ceiling at a relatively high volume. This sets up a broad circulation pattern and maintains the entrainment and air diffusion characteristics necessary to cool the room, while avoiding the unpleasant drafts that would result from merely "blowing" cold air at the room occupants.
On the other hand, for the efficient heating of a cool room, it is often desirable to direct the discharge of the warm supply air vertically downward, at a velocity sufficient to produce a warm air flow at or near the floor level. This minimizes the problem of warm air stratification, and effectively forces the heat into the occupied space. Unfortunately, achieving the necessary air velocity to overcome the warm air stratification is complicated by the fact that many heating systems deliver a reduced volume of warm air (as compared to the volume of cool air delivered in the air conditioning mode).
Some modern linear air diffusers include a control mechanism to accomplish some of these objectives, but most of these require electrical wiring, pneumatic piping or increased system pressure to power the mechanism, thereby limiting their application.